1. Field of the Invention
The present invention relates to a piezoelectric speaker for use in, for example, audio equipment, a method for producing the same, and a speaker system including such a piezoelectric speaker.
2. Description of the Related Art
An audio reproduction mechanism of a piezoelectric speaker is based on planar resonance. Conventional piezoelectric speakers have a structure in which a peripheral portion of a vibrating plate is fixed to a frame. In such a structure, the amplitude of the vibrating plate is significantly reduced toward the peripheral portion of the vibrating plate. As a result,the vibration energy which can be transmitted to the air from the peripheral portion of the vibrating plate is significantly reduced. Such a vibrating plate characteristic is the same as that of the vibration surface of a percussion drum.
For this reason, the conventional piezoelectric speakers have a problem in that a high sound pressure level is obtained in a high frequency range in which sound is reproduced at a relatively small amplitude, whereas a sufficiently high sound pressure level is not obtained in a low frequency range of about 1 kHz or less.
Accordingly, the conventional piezoelectric speaker are only applied, for example, for a tweeter for reproducing sound in a high frequency range and for a receiver of a telephone.
FIG. 22 shows a structure of a conventional piezoelectric speaker 220 including a vibrating plate sandwiched by a resin foam body. The piezoelectric speaker 220 includes a metal vibrating plate 224, a piezoelectric element 223 provided on the metal vibrating plate 224, and a resin foam body 222 for securing a peripheral portion of the metal vibrating plate 224.
The resin foam body 222 has flexibility and is provided so as to hold the metal vibrating plate 224.
The resin foam body 222 provided for increasing the amplitude of the metal vibrating plate 224 also has a contradicting role as a supporting element for securing the peripheral portion of the metal vibrating plate 224. In actuality, the resin foam body 222 is often provided more for securing the peripheral portion of the metal vibrating plate 224 rather than for increasing the amplitude of the metal vibrating plate 224. Accordingly, a sufficient compliance is not obtained.
The vibrating plate 224 of the piezoelectric speaker 220 behaves in a similar manner as that of the vibration surface of a percussion drum, and thus has difficulty in reproducing the sound in a low frequency range as in a conventional piezoelectric speaker in which a peripheral portion of a vibrating plate is fixed to a frame.
The piezoelectric speaker 220 also has an inconvenience that the thickness thereof, which is inevitably increased by the thickness of the resin foam body 222 and a frame (not shown) for holding the resin foam body 222, cannot be reduced to less than a certain level.
As described above, the conventional piezoelectric speakers have a problem of having difficulty in reproducing sound in a low frequency range. The conventional piezoelectric speakers have another problem that since a strong resonance mode is generated in a specific frequency, a large peak dip appears in the acoustic characteristics in a wide frequency range.
According to one aspect of the invention, a piezoelectric speaker includes a frame; a vibrating plate; a piezoelectric element provided on the vibrating plate; a damper connected to the frame and to the vibrating plate for supporting the vibrating plate so that the vibrating plate linearly vibrates; and an edge for preventing air from leaking through a gap between the vibrating plate and the frame.
According to another aspect of the invention, a piezoelectric speaker includes a frame: a plurality of vibrating plates; at least one piezoelectric element provided on the plurality of vibrating plates; a plurality of dampers connected to the frame and to the plurality of vibrating plates for supporting the plurality of vibrating plates so that each of the plurality of vibrating plates linearly vibrates; and an edge for preventing air from leaking through a gap between the plurality of vibrating plates and the frame.
In one embodiment of the invention, the at least one piezoelectric element includes a first piezoelectric element and a plurality of second piezoelectric elements, the first piezoelectric element transmits a vibration to the plurality of vibrating plates, and each of the plurality of second piezoelectric elements transmits a vibration to one of the plurality of vibrating plates which is corresponding thereto.
In one embodiment of the invention, at least a part of a surface of the plurality of vibrating plates is provided with a resin portion thereon.
In one embodiment of the invention, the edge is formed of a resin which is of an identical type as that of the resin portion provided on the surface of the plurality of vibrating plates.
In one embodiment of the invention, the plurality of dampers include a plurality of portions having different physical properties from one another.
In one embodiment of the invention, the edge includes a plurality of portions having different physical properties from one another.
In one embodiment of the invention, the plurality of vibrating plates have different weights from one another.
In one embodiment of the invention, the plurality of vibrating plates are provided with resin layers having different thicknesses from one another.
In one embodiment of the invention, the plurality of vibrating plates have different thicknesses from one another.
According to still another aspect of the invention, a method for producing a piezoelectric speaker, comprising the steps of processing a plate to form a frame, a plurality of vibrating plates, and a plurality of dampers connected to the frame and to the plurality of vibrating plates f or supporting the plurality of vibrating plates so that each of the plurality of vibrating plates linearly vibrates; arranging at least one piezoelectric element on the plurality of vibrating plates; and forming an edge for preventing air from leaking through a gap between the plurality of vibrating plates and the frame.
In one embodiment of the invention, the edge is formed by bonding a sheet to the plurality of vibrating plates.
In one embodiment of the invention, the sheet is an elastic thin rubber film.
In one embodiment of the invention, the sheet is one of an elastic woven cloth and an elastic non-woven cloth, which is filled with a resin having a rubber elasticity by one of impregnation and coating.
In one embodiment of the invention, the edge is formed by holding a liquid polymeric resin in the gap between the plurality of vibrating plates and the frame utilizing a capillary action caused by a surface tension of the liquid polymeric resin.
In one embodiment of the invention, the polymeric resin is one of a solvent volatilization curable resin, a mixture reaction curable resin including at least two types of liquid resin components, and a low temperature reaction curable resin.
In one embodiment of the invention, the polymeric resin is held in the gap by one of dipping and spin-coating.
In one embodiment of the invention, the method for producing a piezoelectric speaker further includes the step of improving an adhesiveness between the plurality of vibrating plates and the polymeric resin before the step of forming the edge.
In one embodiment of the invention, the method for producing a piezoelectric speaker further includes the step of electrically connecting the at least one piezoelectric element.
According to still another aspect of the invention, a speaker system including a plurality of speakers described above.
In one embodiment of the invention, the plurality of speakers have different acoustic characteristics so as to complement a peak dip of one another.
Thus, the invention described herein makes possible the advantage of providing (1) a piezoelectric speaker for reproducing sound in a lower frequency range, a method for producing the same, and a speaker system including such a piezoelectric speaker; and (2) a piezoelectric speaker for restricting a large peak dip from appearing in the acoustic characteristics, a method for producing the same, and a speaker system including such a piezoelectric speaker.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.